What evidence shows that white dwarfs must be very small?

Spectral analysis proposes that there is no hydrogen fusion roughly speaking. They are hot since they are very thick. So if you are a convinced high density and temperature and still not doing synthesis, you must be small. Also, stellar evolution models are founded on the observation of planetary nebulae, where stars have shed most of their mass after being red giants. The physics designates a small, hot, central remainder. 

substitution is the answer in this case

correct answer: understand the different control methods available

integrated pest management is an strategy that is based on the ecosystem and try to prevent the pest and the damage caused by them by applying combination of technique like habitat manipulation, biological control and use of resistant varieties.

the main aim of the integrated pest management is not to completely eliminate the pest but to strengthen the ecosystem so that conditions are favorable for plants and unfavorable for pests.